A conventional umbrella is shown in FIG. 1 and generally includes a shaft having a runner 6 movably mounted to the shaft 1 and a cap 61 is fixed to a top end of the shaft 1. A plurality of ribs 3 are pivotably connected to the cap 61 and a panel 4 is fixedly spread on the ribs 3. Each rib 3 includes a joint 5 connected to a mediate portion thereof and a plurality of stretchers 2 are pivotably connected to the runner 6 and the joints 5 such that when moving the runner toward the cap 61, the panel 4 is stretched outward by the stretchers 2. An inherent shortcoming of the conventional umbrella is hat when wind comes below the panel 4 and goes upward, the remote ends of the ribs 3 cannot stand the force caused by the pressure of the wind and bend upward about the joints 5. This suddenly reduces the area that the panel 4 covers and could damage the joints 5 and the ribs 3.
The present invention intends to provide an umbrella that has a pressure releasing device so as to release the pressure of the wind no matter which direction the wind flows.